Air-assisted fuel injection systems proposed for use on two-stroke engines employ a fuel metering injector that delivers metered fuel to a charge delivery injector. Compressed air is supplied to the charge delivery injector, and when the charge delivery injector is energized, the compressed air carries the fuel into the engine combustion chamber.
The compressed air is usually supplied by an air compressor driven from the engine crankshaft. The air compressor must supply the air required over the entire range of engine operating speeds and thus in many applications must be capable of supplying the required air at engine speeds in excess of 6000 rpm.
An air-assisted fuel injection system supplied by an engine driven air compressor is shown, for example, in international publication WO 88/08082 published 20 Oct. 1988 in the name of P. W. Ragg. As explained there, air compressors capable of supplying the required air flow at high engine speeds may operate inefficiently at the very low engine speeds associated with cranking or starting the engine. When the air compressor is inefficient, an undesirably long period of time may be required to create the pressure in the air supply system necessary for proper fueling of the engine. As a result, a delay in starting the engine may be encountered.